WASHINGTON (Reuters) - A shortened version of a gene may make people more
prone to that sweaty-handed, heart-thumping fear that helped our ancestors
survive, researchers said on Thursday.

People who carry a copy of the short version of the gene react more than
others to scary faces -- and their brains light up correspondingly, a team at
the National Institute of Mental Health reported.

The gene helps brain cells use the protein targeted by anti-depressant and
anti-anxiety drugs called SSRIs. They include Eli Lilly and Co.'s Prozac and
related drugs.

Dr. Daniel Weinberger and colleagues at NIMH found that which version you
carry of the gene helps control how you react to frightening stimuli.

"We have known for a long time that things like temperament are genetic,
present from early in life, and temperament has something to do with how one
responds emotionally to people and places," Weinberger, a neurologist and
psychiatrist, said in a telephone interview.

"We also know from studies in human beings and animals that early childhood
experiences are important in anxiety. This (serotonin transporter) is a genetic
factor that determines how responsive a center in the brain is to stress."

The gene is called SLC6A4, and it codes for a protein that transports the
neurotransmitter, or message-carrying chemical, serotonin from one brain neuron
to another. Serotonin is strongly linked to mood and emotions.

Weinberger's team tested volunteers to see what versions of the gene they
had, and then tested their responses to various stimuli. They used functional
magnetic resonance imaging to show what their brains were doing.

People who had at least one short version of the gene were significantly more
reactive to photographs of frightened faces than people were who had two "long"
copies, the researchers reported in Friday's issue of the journal Science.

"People with two versions (of the short gene) were hard to come by,"
Weinberger added -- but said his team is recruiting and testing people to see if
inheriting a short copy from each parent could make a person unusually anxious.

This is not an "anxiety gene," he said. "There is no one factor that
determines anyone's anxiety proneness." It is more likely that environment and
genetics interact to produce a personality and temperament, he said.

A team at the University of Wisconsin reported last month, for example, that
abused children are more likely to identify "neutral" faces as angry.

Showing people photographs of faces is a time-honored way of judging
emotional reaction, Weinberger said.

"Humans are much more visually oriented (than other animals)," he said. "The
first three months of a baby's life is learning comfort and anxiety based on
familiar and unfamiliar faces."

And, as in all animals, the almond-shaped amygdala seems to be the source of
emotional response in the brain. "It turns on your heart rate, it turns on your
breathing, it turns on your palms sweating," Weinberger said.

"The amygdala learns based on early childhood and other experiences of what
looks dangerous." But a little genetic pre-programming also seems to be going
on.

Now Weinberger's team is looking for other genes that interact with the
serotonin transporter gene. "We are also looking for environmental factors that
interact with this," he said.